The Boring Company’s test tunnel is shaping up well. Elon Musk, the founder of the tunnel-digging venture, shared an image Wednesday of the firm’s Hawthorne, California, construction. It comes after SpaceX’s hyperloop speed competition, just as the firm invites fan competition winners to ride the digging machine “Godot.” Much like the machine itself, Musk’s image came with a cultural reference.

The Boring Company started construction on its first tunnel at the start of 2017, placed at the SpaceX campus, with a view to ultimately make tunneling more efficient and construct a network 30 layers deep in highly congested cities. The firm shared the image on Wednesday with the caption “rings on rings on rings.” Musk described the post as “Wagnerian,” likely a reference to composer Richard Wagner’s “Ring” cycle that consists of four large operas linked by the same story. Perhaps coincidentally, The Boring Company lists four major projects in the works on its website.

The tunnel serves as the test bed for the company’s larger projects. The firm has received an excavation permit to build a 2.7-mile tunnel in Los Angeles that could support 16-passenger transit pods running 30 feet below the surface at speeds of up to 170 mph, with tickets costing $1. Last month, the mayor of Chicago announced the firm would build a similar system to run the 16 miles from the city’s airport to Block 37 downtown — with plans to start digging in just a few months.

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Beyond these three, The Boring Company also proposes a “loop” running the 35 miles between Washington, D.C. and Baltimore. The route, which could extend to New York, is designed so that it could one day receive an upgrade to support Musk’s vacuum-sealed hyperloop system running at up to 700 mph. Over the weekend, SpaceX held its third pod design competition, with the winning team WARR reaching a speed of 290 mph.

As Musk stood behind the podium Sunday and thanked the competition winners for taking part in the hyperloop event, it was a reminder of one of The Boring Company’s other innovations from the “Wagnerian” tunnel. The podium was constructed of bricks made from the dug-up tunnel dirt. Musk previously described the bricks as “rated for California seismic loads, so super strong, but bored in the middle, like an aircraft wing spar, so not heavy.”

Much like Wagner’s “Ring” cycle, The Boring Company has a number of interlocking ideas.